FIELD OF THE INVENTION
The invention relates to a cooling device in an open-end spinning apparatus, having a spinning rotor revolving at high rpm in a rotor housing, a channel plate closing the rotor housing in an operating state, and a yarn draw-off device extending into the spinning rotor.
Open-end spinning apparatuses with cooling devices are known, for instance, from German Published, Non-Prosecuted Application DE-OS 21 59 120. In that spinning apparatus an attempt is made to keep the climatic conditions as constant as possible in the region of the spinning apparatus, by subjecting the spinning apparatus to two separate air flows. A transport air flow that feeds the individual fibers to the spinning rotor simultaneously acts as coolant air for the yarn draw-off region, while an additional cooling air flow cools a bearing region of the spinning apparatus.
It has long been known that in spinning by the open-end rotor spinning process, the attainable rotor rpm is dependent not only on the yarn tension forces involved but also on the temperature at the yarn draw-off nozzle.
When processing synthetic fibers, especially polyester fibers or mixtures of natural and synthetic fibers, the operating speeds of such open-end rotor spinning machines are therefore limited. Open-end spinning machines cannot be operated at the theoretically attainable high rotary speeds, since damage to the synthetic fibers would then occur from overheating, caused by the heat of friction. It is therefore usual, when synthetic fibers are to be.sup.I processed, to operate open-end rotor spinning machines at reduced speed, or in other words not at the maximum possible rotor rpm. In comparison with the theoretically attainable rotor rpm, that represents a considerable loss in production, since the production of an open-end rotor spinning machine is directly proportional to the rotor rpm. Although that problem of damage to synthetic. fibers or chemical fibers has long been known, until now no satisfactory solution has been found.
It is known, for instance, from German Published, Prosecuted Application DE-AS 24 10 940, to aim a cooling air flow at a yarn guide funnel, which is comparable in function to a yarn draw-off nozzle. However, that has not led to a usable solution to the problem.
German Published, Non-Prosecuted Applications DE 40 07 517 A1 and DE 41 19 264 A1 also disclose dissipating the heat of friction-that occurs in the region of the yarn draw-off nozzles by means of special heat dissipating nozzles, thereby avoiding damage to the fibers. For technical reasons in spinning, the generation of the heat of friction, which depends on the coefficient of friction, the normal force between the yarn and the contact surface of the draw-off nozzle, and the sliding speed, cannot be decreased substantially. Therefore, in the references mentioned above, yarn draw-off nozzles that have a high heat dissipation value lambda being greater than 80 W/mK are employed. However, the service life of such draw-off nozzles is limited.